Multiple cathode display tube

ABSTRACT

The drawing discloses a tube which includes a large number of cathode rods arrayed in rows and enclosed in cavities in a stack of plates including, from bottom to top, a metal focusing plate for controlling the location of glow on the cathode rods, an opaque insulating disk, an opaque disk shaped to trap cathode sputtering and to prevent the spread of cathode glow from one cathode aperture to an adjacent aperture, and an anode plate.

United States Patent Maloney 1 Mar. 21, 1972 [54] MULTIPLE CATHODE DISPLAY TUBE [72] Inventor: Thomas C. Maloney, Bernardsville, NJ.

[73] Assignee: Burroughs Corporation, Detroit, Mich.

[22] Filed: Mar. 4, 1969 21 Appl. No.: 806,020

Related U.S. Application Data [63] Continuation-impart of Ser. No. 618,138, Feb. 23,

1967, abandoned.

[52] U.S. Cl ..313/109.5, 313/209, 313/210 [51] lnt.Cl ..H0lj 61/04, HO1j61/10,H0lj61/64 [58] Field of Search ..315/169, 169 TV, 84.5;

[56] References Cited UNITED STATES PATENTS 2,858,489 1 19 Shadowitz .3 3/2o9x 3,225,251 12/1965 Van Paassen et al. ..313/210 X 3 ,260,880 7/1966 Kupsky ..313/109.5 3,315,115 4/1967 Maloney.... .313/109.5 X 3,346,759 lO/l967 Hardwick ..313/210 X Primary ExaminerJames W. Lawrence Assistant Examiner-Palmer C. Demeo Att0rney-Kenneth L. Miller and Robert A. Green [5 7] ABSTRACT The drawing discloses a tube which includes a large number of cathode rods arrayed in rows and enclosed in cavities in a stack of plates including, from bottom to top, a metal focusing plate for controlling the location of glow on the cathode rods,

an opaque insulating disk, an opaque disk'shaped to trap cathode sputtering and to prevent the spread of cathode glow from one cathode aperture to an adjacent aperture, and an anode plate.-

12 Claims, 4 Drawing Figures PATENTEUMARZI I972 sum 1 [IF 2 oovooooovoooonv o ooonooooooooo A INVENTOR T. C. MflLO/VE Y ZMG,

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INVENTDR T. C. MHLOALE Y MULTIPLE CATHODE DISPLAY TUBE This application is a continuation-in-part of application Ser. No. 618,138, filed Feb. 23, 1967, and now abandoned.

BACKGROUND OF THE INVENTION number of tiny glow cathodes whose light output is generally proportioned to the current thereto, the cathodes being close together and mounted to prevent light from one cathode from seeming to emanate from adjacent cathodes.

SUMMARY OF THE INVENTION Briefly, a cold cathode glow tube embodying the invention includes a plurality of tiny rodlike cathodes which are positioned in cavities in a metal focusing plate which is operated at such a potential that the cathode glow tends to be focused at the tip of each cathode for optimum efficiency. The tube also utilizes an electrode assembly which includes an anode plate and various other plates shaped to trap sputtered cathode material and to prevent the lateral dispersion of light from a cavity containing a glowing cathode to adjacent cavities wherein the cathode may or may not be glowing.

DESCRIPTION OF THE DRAWINGS FIG. 1 is a plan view of a multiple cathode glow tube embodying the invention;

FIG. 2 is a sectional view of the tube ofFIG. 1;

FIG. 3 is a sectional view similar to that of FIG. 2 showing a portion of a tube embodying a modification of the invention; and

FIG. 4 is similar to FIG. 3 and shows another modification of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION The tube of the invention includes a gas-filled envelope 18 which has a glass stem 20. The envelope 18 includes a transparent viewing window 22. The stem 20 is provided with a tubulation suitably positioned near its periphery so as not to interfere with other tube components oriented at the center of the tube. The stem also carries a plurality of alignment and mounting pins spaced apart near its periphery, an anode pin and a focusing electrode pin 60. The pins 50 and are also positioned near the periphery of the stem, preferably remote from each other. Those skilled in the art will understand how to mount and align the various tube electrodes (to be described) on pins 40 and how to properly insulate the electrodes from the various pins where required. Accordingly, in order to simplify the drawing, some of these features are omitted.

The stem 20 is also provided with a plurality of cathode pins 70, and, in one embodiment of the invention, two rows of closely spaced cathode pins are provided with the pins staggered as shown in FIG. 1. This arrangement provides an illusion of a single row of contiguous cathodes while maintaining sufficient spacing between the actual cathodes to prevent cross-talk between them through the electrode assembly sur- Disk is also provided with a cutout slot in its lower surface 94 and a plurality of cathode apertures which extend from the slotted area 110 to the upper surface of the disk. The cathode apertures 120 are positioned to receive the cathode pins 70. The relative thickness of the plate 90 and the length of the cathode pins is such that the pins project into the apertures 120 but do not extend as far as the top surface 92 thereof.

The electrode assembly next includes an opaque insulating (mica) disk seated on the top surface 92 of the conductive disk 90 and provided with suitable apertures (not shown) to receive the mounting pins 40 and at least the anode pin 50, and apertures which permit the cathodes 70 to be viewed when they glow. The cathode apertures 160 are smaller in diameter than the cathode apertures 120 in the disk 90 to pro vide a trap arrangement for sputtered cathode material.

The next element in the electrode assembly is an opaque plate which may be either insulating or conductive and is seated on the mica disk 140. The plate 170 has an aperture for each cathode electrode and other appropriate alignment and mounting apertures (not shown). The cathode apertures 180 in plate 170 are of larger diameter than the corresponding apertures in the mica disk 140 to form part of the arrangement for trapping sputtered cathode material and thus preventing the formation of conductive leakage paths between one metal disk and another in the electrode assembly.

Another opaque metal plate which is the anode in the tube 10 is seated on plate 170. The anode plate 190 has the usual mounting apertures (not shown) and an aperture for receiving the anode pin 50 which is suitably connected thereto and cathode apertures 193 of a suitable size and shape, preferably smaller than apertures 180 in plate 170. If con- I venient, plates 170 and 190 may be made as one piece. The

electrode assembly also includes an insulating mica disk 195 on anode plate 190 and a holddown metal or insulating plate 200 seated on the mica disk 195. Mica disk 195 and holddown rounding the cathodes. The illusion of continuity of glow is especially apparent when the rows of cathodes are scanned by an oscillating mirror in one mode of operation.

The electrode assembly of tube 10 includes the following elements. First, a washer 80 is placed on each of the mounting posts 40, and a conductive disk 90, a focusing electrode, is seated on the washers. The washers provide thermal isolation between disk 90 and the glass stem 20. The conductive disk 90 has to and bottom surfaces 92 and 94 and is provided with suitable apertures (not shown) for each of the mounting pins 40 and the two electrode pins 50 and 60. Pin 60 is in electrical contact with disk 90 by a press fit or by welding or the like.

plate 200 include suitable apertures to receive the mounting pins 40 and any other pins, and large central cutout portions 220 through which the cathodes can be viewed.

The entire assembly of plates is secured together by means of eyelets 221 crimped on the mounting pins 40 and in contact with holddown plate 200, either directly or through insulating spacers as required. Of course, the anode pin 50 and focusing electrode pin 60 may extend through the stack of plates and may be used for alignment purposes, if desired.

It is noted that the apertures in the various plates combine to form a viewing cavity or chamber for each cathode, and the diameter of each cavity is properly varied above the cathode pins to provide a sputter trap for each cathode.

The completed tube 10 includes a suitable gas for sustaining cathode glow, such as neon, argon, or the like at any suitable pressure, for example 50 to 100 mm. of Hg at room temperature. The gas atmosphere may also include agents such as mercury to minimize cathode sputtering and a radioactive gas such as Krypton 85 to facilitate the initiation of cathode glow.

As noted above, where parts must be insulated from each other, suitable precautions are taken to provide such insulation. For example, the anode pin is held insulated from all of the other metallic elements in the tube assembly, for example, by being coated with insulating material or by means of suitably large apertures in the other plates which prevent the anode pin from making contact with these plates.

It is well known that cathode sputtering occurs in cold cathode glow tubes, and, under some circumstances, precautions must be taken to prevent the formation of continuous paths of sputtered metal which might cause shorts between adjacent metallic members. One precaution comprises the provision of mercury in the gas atmosphere within the envelope. This mercury may be provided in the gas filling directly, or it may be admitted by way of an auxiliary capsule provided in the envelope. Normally, this expedient inhibits substantially all cathode sputtering during normal tube operation. However, it may be desirable to include other means for minimizing the adverse effects of cathode sputtering which may occur during tube processing.

The step arrangement in the cathode cavities for preventing shorts between plates has already been described. Another area to be protected is the surface of the stem 20 which faces focusing electrode 90 in the vicinity of the cathode pins. One suitable protective arrangement here comprises raising the electrode 90 a suitable distance above the stem. In another expedient to prevent the formation of continuous leakage paths on the glass stem, the stern might be roughened or dimples 251 might be provided suitably positioned with respect to the cathode pins to break up sputtered metal paths which might form on this surface. Another arrangement comprises the provision of slot 110 and the filling of this slot with an opaque fibrous material 252 such as ceramic wool or the like which would serve to trap sputtered material. This would have the added advantage of preventing the spread of light from one cathode cavity to another under plate 90. In addition, the cathode pins below the desired glow area might be coated with a suitable material to prevent glow and thus prevent sputtermg.

In one typical'construction, two rows of 28 cathodes each were employed with each cathode rod having a diameter of 0.020 inch, the cathode apertures in plate 90 having a diameter of 0.037 inch, and the center to center spacing between any two adjacent cathodes being 0.046 inch.

In one mode of operation of the tube 10, each cathode is coupled through appropriate circuitry to a remote sensing element which senses a condition and provides at its cathode a resultant current flow which produces a corresponding light intensity. If all of the cathodes are scanned by an oscillating mirror, an array of closely spaced lines of light are produced, and if simultaneously, the light output of each cathode is varied in intensity, a meaningful picture having light and dark areas of different intensities is produced and is visible in the mirror. Optimum operation within this framework is obtained if cathode glow is maintained or focused near the tip of each cathode rod. This represents an initial setting so that in operation, if current flow increases, cathode glow might spread a little, but the primary change is in the intensity of glow. This is achieved in tube by suitably selecting the gas pressure and the distance between each cathode rod and the adjacent focusing electrode 90 in accordance with the well-known Paschen P (Pressure) D (Distance) curve. In addition, the potential applied to the focusing electrode 90 affects the location of the glow. Typically, the potential on the electrode 90 is slightly lower than anode potential, and, in one tube construction using an anode potential of about 280 volts, the focusing potential was about 260 volts.

In a modification of the invention illustrated in FIG. 3, each of the cathode pins 70 has a free leading end portion 250 positioned within its aperture 120 in plate 90. Cathode portion 250 is intended to produce glow and the remainder 260 of each cathode pin extending from portion 250 through the stem is coated with a layer 270 of an insulating material such as glass. This glass coating 270 limits the spread of cathode glow during tube operation. The cathode pins are sealed in apertures 280 in the stem by means of an insulating cement 290 such as Pyroceram. Since Pyroceram is fluid in its uncured state and whenit is applied to the stem during tube manufacture, a plate 300 of insulating material such as mica is provided between plate 90 and the top surface of the stem to prevent the Pyroceram from entering the apertures 120 in plate 90. The mica plate 300 includes small apertures through which the cathode pins extend. All of the otherplates shown in the electrode assembly in FIG. 2 are also employed in the tube of FIG. 3.

A modification of the invention shown in FIG. 4 uses the tube shown in FIG. 3 and adds thereto a small diameter hollow metal sleeve 310 secured to the free end portion 250 of each cathode rod. The metal sleeves provide cathode structures which operate with the hollow cathode effect and thereby provide more intense light output than the bare cathode pins 70.

The tube of FIG. 4 is arranged mechanically, that is, with electrode spacings, gas pressure, etc., so that cathode glow takes place on the inside of each cathode sleeve 310, and not on the outside. In one tube construction, the metal sleeves had a diameter of 0.021 inch, a length of 0.050 inch, and the upper edge was 0.040 inch below the top surface of plate 90. In addition, the cathodes and the sleeves were spaced 0.005 inch from the adjacent wall of plate 90. The tube had a gas pressure of about 30 mm. Hg at room temperature.

In the tube of FIG. 4, since cathode glow occurs inside the cathode sleeves, problems due to the sputtering of cathode metal onto adjacent surfaces would generally be minimized. As a result, the array of plate apertures shown in FIG. 2 for trapping sputtered metal may not be required. However, as a security measure, it would be well to include this sputter trap arrangement.

What is claimed is:

1. A multiple glow cathode display tube comprising an envelope having a stem containing a gas suitable for exhibiting cathode glow and having a viewing window,

a plurality of rod-like glow cathodes sealed in and extending through said stem and extending into said envelope,

an electrode assembly in said envelope including, in order, a

metallic plate operable as a cathode glow focusing electrode and having an aperture for each cathode, an opaque insulating shield assembly including an aperture for each cathode, and an anode plate having an aperture for each cathode,

all of said cathode apertures being aligned to form a separate continuous viewing chamber for each cathode and through which each cathode can be viewed from outside said envelope and through said viewing window, said continuous viewing chambers having regions of different diameter positioned so that each operates as a trap for sputtered cathode material.

2. The tube defined in claim 1 wherein said electrode assembly is in the form of a sandwich of plates, and a plurality of mounting pins extend through said stem and through said plates to hold them aligned in position.

3. The tube defined in claim 1 wherein said continuous chambers are of substantially constant diameter except for a region of enlarged diameter positioned between the ends of said rod-like glow cathodes and said viewing window.

4. The tube defined in claim 1 wherein said rod-like cathodes extend into said cathode glow focusing electrode.

5. The tube defined in claim 4 wherein each of said continuous chambers is of substantially constant diameter except for a region of enlarged diameter positioned between said focusing electrode and said viewing window.

6. The tube defined in claim 1 wherein said electrode assembly is opaque to prevent the glow of one cathode from spreading to an adjacent cathode.

7. The tube defined in claim 1 and including means preventing the spread of light from one cathode chamber to an adjacent cathode chamber.

8. The tube defined in claim 1 wherein, in said electrode assembly, each cathode aperture in said shield assembly includes an irregular surface formation positioned to receive sputtered material from said cathodes and to prevent the formation of continuous conductive paths between cathodes.

9. The tube defined in claim I wherein said metallic plate includes a lower surface which faces the stem of the envelope, said lower surface of said metallic plate having a cutout portion in the region thereof through which said cathode electrodes extend, said cutout portion including means to prevent the spread of light from one cathode chamber to another.

10. The tube defined in claim 9 wherein said last-named means comprises an opaque porous material which presents a rough surface to said cathodes.

11. The tube defined in claim 1 and including a hollow metal tube secured to the end of each rod-like glow cathode, said tube being adapted to provide hollow cathode operation. 

1. A multiple glow cathode display tube comprising an envelope having a stem containing a gas suitable for exhibiting cathode glow and having a viewing window, a plurality of rod-like glow cathodes sealed in and extending through said stem and extending into said envelope, an electrode assembly in said envelope including, in order, a metallic plate operable as a cathode glow focusing electrode and having an aperture for each cathode, an opaque insulating shield assembly including an aperture for each cathode, and an anode plate having an aperture for each cathode, all of said cathode apertures being aligned to form a separate continuous viewing chamber for each cathode and through which each cathode can be viewed from outside said envelope and through said viewing window, said continuous viewing chambers having regions of different diameter positioned so that each operates as a trap for sputtered cathode material.
 2. The tube defined in claim 1 wherein said electrode assembly is in the form of a sandwich of plates, and a plurality of mounting pins extend through said stem and through said plates to hold them aligned in position.
 3. The tube defined in claim 1 wherein said continuous chambers are of substantially constant diameter except for a region of enlarged diameter positioned between the ends of said rod-like glow cathodes and said viewing window.
 4. The tube defined in claim 1 wherein said rod-like cathodes extend into said cathode glow focusing electrode.
 5. The tube defined in claim 4 wherein each of said conTinuous chambers is of substantially constant diameter except for a region of enlarged diameter positioned between said focusing electrode and said viewing window.
 6. The tube defined in claim 1 wherein said electrode assembly is opaque to prevent the glow of one cathode from spreading to an adjacent cathode.
 7. The tube defined in claim 1 and including means preventing the spread of light from one cathode chamber to an adjacent cathode chamber.
 8. The tube defined in claim 1 wherein, in said electrode assembly, each cathode aperture in said shield assembly includes an irregular surface formation positioned to receive sputtered material from said cathodes and to prevent the formation of continuous conductive paths between cathodes.
 9. The tube defined in claim 1 wherein said metallic plate includes a lower surface which faces the stem of the envelope, said lower surface of said metallic plate having a cutout portion in the region thereof through which said cathode electrodes extend, said cutout portion including means to prevent the spread of light from one cathode chamber to another.
 10. The tube defined in claim 9 wherein said last-named means comprises an opaque porous material which presents a rough surface to said cathodes.
 11. The tube defined in claim 1 and including a hollow metal tube secured to the end of each rod-like glow cathode, said tube being adapted to provide hollow cathode operation.
 12. The tube defined in claim 1 wherein the surface of said stem in the vicinity of said cathode rods is provided with surface discontinuities to prevent the formation of continuous conductive paths of sputtered cathode metal. 